Monitoring
Measuring the success of Whangarei Harbour Marine Reserve
Making a marine reserve takes considerable time, effort and resources from dedicated members of the community and government bodies. The goal of a marine reserve is to set aside a piece of the marine environment to function as naturally as possible, and to allow a marine eco-system to improve and recover.
View from Reotahi waterfront
The success of a marine reserve is dependant on a number of factors; most importantly support from the community, but also size, impact of fishing around the borders, location and habitat representation.
The Department of Conservation aims to test the success of the Whangarei Harbour marine reserve by establishing a biological monitoring program.
The state of the marine environment was measured to start with; this is called capturing a biological baseline. After the marine reserve has been in place for a few years further surveys will be carried out to measure change over time.
In this way DOC can test, for example, if the position of the marine reserve boundary is accomplishing marine biodiversity protection, if the reserve is too small, or if other factors are continuing to have a detrimental impact on the natural ecology of the reserve.
Waikaraka
The relative role of harvesting versus environmental degradation impacts on the Waikaraka marine environment are unknown but it is likely environmental degradation has played the key role in altering the ecology of the system. Approximately 5% of the marine reserve is sub-tidal and sediment inputs from Portland cement and dredging were estimated at 20 times natural levels between 1958 and 1980 (Millar, 1980).
Fishing ceased once the marine reserve was established however inputs from forestry, contaminants and runoff in the surrounding catchment continue to impact on the area. The success of this marine reserve is reliant on integrated catchment management and the Department of Conservation hopes the marine reserve will act as a focal point for conservation and restoration efforts in the harbour.
Because of these continuing impacts and the typical, intertidal, mangrove, marine environment at Waikaraka, collecting a biological baseline to resolve future change is difficult.
Typical methods for measuring the abundance of fish and invertebrates species in soft sediment environments are invasive i.e. organisms are killed during sampling, with nets and sieves and aren't appropriate for marine reserves. Techniques can also be expensive because a high level of expertise is required to identify diverse macro-invertebrate assemblages. Changes in biological communities may also be sudden due to catastrophic events such as large and rapid inputs of sediment fines into the system from, e.g. a rain event, coinciding with forestry clear felling in the catchment.
This means biological baseline information using the abundance of organisms must be interpreted in relation to the magnitude of recent and historical sediment and contaminant inputs. Because these impacts have been ongoing since the early 1900s, any future change, positive or negative will happen over long time frames.
Habitat map of the Whangarei Harbour
Marine Reserve (view larger, JPG, 107K)
DOC decided on an alternative, more cost effective approach to collecting biological baseline information. Aerial photography has been used to map the current state and boundaries of salt marsh, mangrove, stream, inter-tidal and subtidal environments. Urban runoff and sediment inputs from foresty and urban development in the surrounding catchments are likely to continue to impact on this marine reserve. Habitat maps and aerial photography will assist in providing information about the effects of these impacts over time.
Reotahi - Motukaroro Island
Reef fish and crayfish are monitored at Reotahi and non-reserve control sites located nearby. The outside sites or 'fished reference sites' are intended to provide a means of comparison overtime between the normally fished state and the fully protected reserve sites.
Care was taken to locate reference sites with similar current, bottom type and depth to the reserve sites. This proved difficult because of the unique Motukaroro marine environment.
Marine scientists were contracted to undertake a baited underwater video technique; recognised as the best current non-invasive method for measuring the abundance and size of carnivorous fish species. The system consists of a high resolution colour camera in a waterproof housing positioned 1.5 m above a bait container holding four pilchards. Fish are attracted to the bait and can be recorded, counted and measured.
Divers will also carry out underwater visual census of reef fish assemblages and crayfish in March 2007 before any effects of marine protection are likely to have happened. Marine habitats in the reserve and control sites have also been mapped using aerial photography, sidescan sonar, underwater video, underwater still photography and diver surveys.
The University of Auckland has carried out studies at Motukaroro Island for many years. Second year ecology students have been visiting Motukaroro Island each year since the early 1980s to study and compare patterns of zonation between exposed and sheltered shores. These trips will continue into the future.
The public are being encouraged to visit and to study the diverse marine life at Waikaraka and Reotahi. The public are also being encouraged to keep a lookout for six exotic high impact species identified by the Ministry of Fisheries to threaten New Zealand's ecology (Find out more on the Biosecurity New Zealand website).
Motukaroro Island is located opposite the Marsden Point port, the closest port to the majority of New Zealand's international markets. Ballast water and hull fouling pathways may be acting as vectors for potentially invasive species. A watching brief will be kept for these species by DOC during monitoring investigations.
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